The present invention relates generally to the field of industrial furnace and boiler fossil fuel burners and in particular to a new and useful burner swirler with openings in the trailing edge of the swirler blades for liquid fuel atomization and injection into the combustion mix.
Conventional fuel oil atomizers consist of a single centerline pipe or barrel through which a liquid fuel and atomizing substance (typically steam) flow concentrically toward a mixing chamber and subsequently to a multi-hole sprayer cap. Holes are drilled in the sprayer cap to create a radially diverging spray pattern in the shape of a cone. Atomizers are generally positioned in the center of burners where swirling combustion air is provided for burning the liquid fuel. In some cases, a bladed swirler is also installed adjacent to the sprayer cap to mix the combustion air with the fuel spray.
Oxygen-enriched combustion and full substitution of air with oxygen have gained considerable attention for their demonstrated low emissions and high combustion efficiency improvements over the air-blown operation. Oxygen can be introduced into the combustion zone in several ways.
In a multi-annulus burner, oxygen can be introduced by premixing it with combustion air, recirculated fuel gas, overfire air, or by direct injection via lances.
In an oil-fired burner, oxygen can also be used as the atomizing medium in the fuel atomizer instead of steam or compressed air.
Burning fossil fuels generates NOx from the oxidation of fuel-nitrogen content and/or direct oxidation of atmospheric nitrogen in the combustion air. NOx is a known precursor to acid rain, photochemical smog and air pollution in general. Various methods have been formulated to reduce NOx emissions. One such NOx reduction method involves the use of natural gas in fossil fuel burners.
As taught by U.S. Pat. No. 5,807,094, an air-premixed natural gas burner is provided which has reduced NOx formation resulting from partial pre-mixing of air and natural gas adjacent to the burner throat. The entire disclosure of U.S. Pat. No. 5,807,094 is incorporated herein by reference.
U.S. Pat. No. 5,470,224 discloses a burner having natural gas injected between the blades of an air swirler for rapid mixing.
U.S. Pat. No. 5,829,369 describes the use of axial natural gas elements for co-firing fuel gas with pulverized coal.
In fossil fuel-burning boilers, fuel and air enter into the furnace to mix and burn. Low-NOx burners operate on the principle of controlled separation and mixing of the fuel and oxidizer. Internally staged burners minimize the early mixing between oxygen-rich air and fuel streams during fuel pyrolysis, so that the nitrogenous compounds in the fuel convert to N2 rather than NOx. Externally staged burners operate with even less oxidizer in the main combustion zone to minimize NOx formation since part of the total oxidizer is diverted and re-introduced into the furnace downstream of the burner zone through the overfire (OFA) ports.
Fuel reburning is also used for NOx reduction (up to 30% fuel reburn). It involves injecting a supplementary fuel (e.g., natural gas, fuel oil, or pulverized coal) with air above the generally oxygen-rich (stoichiometric ratio, SR≧1.0) main flame zone to create a locally oxygen-deficient reburn zone (SR<1.0). In the reburn zone, the supplementary fuel generates hydrocarbon radicals, amines, and cyanic species that react with the incoming main combustion zone products to convert NOx to N2. Additional air is introduced through the OFA ports above the reburn zone to complete the burning of the combustible matter. In some applications, a part of the flue gas from downstream of the boiler exit is re-circulated into the reburn burner. Flue gas re-circulation (FGR) provides a means for transporting the reburn fuel into the furnace. It also helps to reduce NOx by quenching the local reaction zone.